Various types of radiating cables are used for transmission and propagation of electromagnetic signals. Radiating cables generally have a coaxial cable that includes an inner conductor surrounded by an outer conductor of tubular form, and a dielectric layer interposed between the two conductors. The outer conductor includes slots which generate an electromagnetic radiation. The outer conductor is covered by an insulating outer sheath.
The slots in the outer conductor may be of various types, for example a longitudinal slot over the entire length of the cable, or numerous small holes very close to each other. The radiating cables may operate in a “coupled mode” or a “radiated mode.” In a coupled mode, the total length of the outer conductor includes slots that are separated by a distance considerably shorter than the wavelength of the radiated signal, and the radiated energy propagates in a direction parallel to the cable. With these cables, the signal received by a receiving antenna dissipates rapidly when the distance between the antenna and the cable increases, and the received signal fluctuates greatly when the receiving antenna is moved along a path parallel to the cable. In a radiated mode, the outer conductor includes groups of slots, which are reproduced with a constant spacing, this spacing being of the same order of magnitude as the wavelength of the signal to be radiated.
The outer conductor is typically prepared by punching holes in a suitable metal strip before folding the strip around the dielectric spacer. The pre-punched metal foil wrapped around the dielectric spacer is not welded and/or bonded. Moreover, a problem associated with the manufacture of radiating coaxial by wrapping the punched metal strip around the dielectric spacer is mechanical slot compression. During wrapping, the slots are compressed in the circumferential direction with respect to the cable causing the slots to become narrower. This mechanical slot compression results in less slot area through which the cable can emit or receive a signal. This impacts the efficiency of the radiating cable and mechanical strength.
The provision of slots in the outer conductor, before wrapping can affect the mechanical properties of the cable as well. For example, the slotted conductor metal sheet may be less resistant to kinking and crushing during handling and installation of the cable. Further, the resistance to environmental conditions such as moisture ingress into the dielectric core can also be reduced. Each of these problems may lead to electrical degradation of the cable.